The present invention relates to a rotary drive device, comprising a housing element, a drive shaft which is rotatably mounted in the housing element, a driven shaft which is rotatably mounted in the housing element, and a transmission device for transmitting a torque from the drive shaft to the driven shaft.
Rotary drive devices of this type are generally known. Said devices can be used firstly to provide a rotational movement on the driven shaft, which then drives additional components of a superordinate construction, or for example also in cooperation with a device for converting the rotational movement of the driven shaft into a longitudinal movement, such as a worm gear or the like. Variable-length units of this type, in which a rotational movement of a drive shaft is converted by means of a driven shaft and furthermore a device for converting the rotational movement into a longitudinal movement for varying the length of the unit as a whole, are used in particular in motor vehicles, for example for closing and opening engine bonnets, tailgates, luggage-compartment lids, doors and similar pivotable elements.
In known generic devices, however, no mechanism is provided which provides, according to a difference in torque between the drive shaft and the driven shaft, a braking force against the rotational movement of the drive shaft or driven shaft in the rotary drive device. However, it has been found that in particular there is a need for a rotary drive device in which, when the difference in torque increases, a decreasing braking force is provided according to the above-mentioned difference in torque between the drive shaft and the driven shaft, so that the rotary drive is braked strongly in the case of a low “stress” between the drive shaft and the driven shaft, i.e. for example between the motor which is assigned to the drive shaft and the component to be driven which is assigned to the driven shaft, whereas in the case of a high “stress” between the above-mentioned components, the braking effect is reduced or even completely eliminated.